1. Field of the Invention
The present invention relates generally to optical fiber, and particularly to dispersion compensating optical fibers and systems employing same.
2. Technical Background
Increased demand for higher bit transmission rates has resulted in a large demand for optical transmission systems that can control and minimize dispersion effects. Analysis of common optical transmission systems indicates that while optical transmission systems can tolerate fairly large amounts of residual dispersion at 10 Gbit/second, these systems can tolerate only small amounts of residual dispersion at higher transmission rates of about 40 Gbit/second without causing unwanted signal distortion. Therefore, it is of the utmost importance to accurately control dispersion in such high bit-rate optical transmission systems across the entire wavelength band of interest. Moreover, dispersion control becomes increasingly important as the transfer rate increases. In addition to the need to accurately control dispersion, it is also desirable to compensate for dispersion slope of the transmission fiber as transmission rates approach 40 Gbit/second.
Various solutions have been proposed to achieve the dispersion and dispersion slope values required for compensating standard single mode optical fibers. One favored approach involves housing a dispersion compensating fiber in a dispersion compensating module wherein accumulated dispersion of the transmission fiber is compensated for at the end of the fiber span where the fiber end is accessible. Such modules include a length of dispersion compensating fiber wound onto a spool or reel.
One example of a dispersion compensating fiber used to compensate for standard single mode fiber, such as SMF-28® manufactured and marketed by Corning Incorporated of Corning, N.Y. is described in U.S. Patent Application 2003/0053780. Only a relatively short length of this dispersion compensating fiber is required to compensate for an approximately 100 km length of standard single mode transmission fiber at 1550 nm.
Two important parameters in dispersion compensating modules are Figure of Merit (FOM) and Insertion Loss (IL). As the length of dispersion compensating fiber required to compensate for the dispersion of the transmission fiber increases, so does the attenuation contributed thereby, and, thus, so does insertion loss. Typically, the main contribution to IL is the attenuation of the dispersion compensating fiber itself. FOM is the ratio of the absolute value of dispersion at 1550 nm divided by fiber attenuation at 1550 nm. A high FOM number is desirable, as it is a measure of how much loss is induced by addition of the dispersion compensating fiber to compensate for the accumulated system dispersion of the span including the standard single mode fiber.
Thus, there is a need for a dispersion compensating fiber for compensating dispersion in spans of standard single mode fiber which has increased FOM and lower IL such that the fiber introduces less loss while compensating for accumulated dispersion in the system.